The present invention relates to processes for treating nitric-containing effluents from nitric acid production plants or nitric acid-using plants, such as hydrometallurgical treatment plants for cobalt or for uranium ores, and more specifically it relates to novel treatment methods which permit recovery of the nitric values.
Effluents containing nitric acid and nitrate ions cannot be discharged as such without risk of pollution by said ions. Hence, numerous methods of treating said effluents have been proposed. Noteworthy among the latter is the method described in French Pat. No. 2,087,565 of the Commissariat a l'Energie Atomique (French Atomic Energy Commission). According to this method, the effluent is treated with calcium hydroxide and the resulting calcium nitrate is treated with sulfuric acid; in this way one obtains, depending on the conditions, ammonia, calcium sulfate (which precipitates), and nitric acid. This method has the disadvantage of creating a dilute solution of nitric acid which cannot be recycled without burdensome concentration.
Other methods have been proposed, including the method described in the article "Recuperation de l'acide nitrique par extraction par solvant" ("Recuperation of Nitric Acid By Solvent Extraction"), BIST (Commissariat a l'Energie Atomique--French Atomic Energy Commission), No. 185, Oct. 1973. This method which involves extraction by a solvent (tributylphosphate) has the disadvantage of producing a dilute nitric acid, whilst necessitating a large number of extraction stages.